The field of aerodynamic design for projectiles, aircraft, rockets and the like is extensive. The physical size of small caliber bullets/projectiles presents challenges not encountered in aircraft wing, ballistic missile, artillery shell or aircraft delivered bomb design. For small caliber weapons like handguns, shotguns, rifles and machine guns, performance enhancements have for decades been incremental at best.
The search for improved performance in handgun cartridges with better bullet external balistics and terminal effects continues unabated. It is not uncommon for Law Enforcement organizations to have issued 9 mm Luger/Parabellum (9×19 mm) semi-automatic duty pistols in the 1990's only to change to 40 Smith & Wesson caliber (10×22 mm) in the 2000's and now are reverting back to the 9 mm Luger. The reasons for changing back to the 9 mm from the 40 S&W include:                advances in 9 mm bullet design,        increased muzzle energy in +P loadings,        reduced recoil versus 40 S&W, 357 SIG and 45 ACP        longer service life of the weapon,        quicker and more accurate follow up shots due to reduced recoil,        lower cost ammunition and others.        
Another distinct advantage of the 9 mm Luger is its smaller case diameter, which results in greater magazine capacity versus similar sized pistols chambered in 40 S&W (based on the 10 mm Auto case dimensions), 357 SIG (Schweizerische Industrie-Gesellschaft, also based on the 10 mm Auto case dimensions), 10 mm Auto, 38 Super (semi-rimmed case) and 45 ACP (Automatic Colt Pistol) pistols. Recent reports from the FBI (Federal Bureau of Investigation) affirm that the terminal effects and wound damage for modern 9 mm Luger cartridges/bullets versus 40 S&W and 45 ACP are essentially the same.
The 9 mm Luger is considered to be the most popular centerfire pistol cartridge in the world. The 9 mm Luger, aka 9 mm NATO (North Atlantic Treaty Organization), is the standard center fire pistol cartridge for the US military and its NATO allies. However during the summer of 2014, the US Army announced a new pistol procurement program known as the Modular Handgun System. The program intends not only to replace approximately 400,000 Beretta M9 and SIG Sauer M11 pistols, but is seeking alternative cartridges to the 9 mm NATO.
Different than Law Enforcement engagements, the military can frequently encounter soft body armor or thick clothing that the 9 mm Luger fails to effectively penetrate. Spokesmen for the Modular Handgun Caliber procurement have stated that the replacement caliber “ . . . must exceed the performance of the current M882 9 mm round.” and “ . . . provide the soldier with increased terminal performance,” and “feedback from soldiers in the field is that they want increased ‘knock-down power.”
The difference in ballistic efficiency for the same projectile diameter used in common handguns and rifles is vast. Handgun projectiles are typically designed for close range and rifles for more distant targets. The different applications affect the overall size of the weapon, bullet shape, bullet diameter, bullet length, cartridge overall length, magazine capacity and projectile performance. For example, common 30 caliber bullets for handguns have a diameter from 0.309 to 0.312 inches, weigh from 80 to 110 grains and have ballistic coefficients of around 0.100 to 0.150.
Common 30 caliber bullets for rifles have a diameter from 0.303 to 0.311 inches, weigh from 110 to 220 grains and have ballistic coefficients of around 0.250 to 0.450. The lower the ballistic coefficient, the quicker the bullet loses velocity and useful range. Nose profile or shape, ratio of bullet length to diameter, shape of the end of the projectile and other design aspects significantly affect the ballistic coefficient. Typically handgun bullets are larger in diameter than rifle bullets. The 30 caliber cartridges best illustrate the performance variations between handgun and rifle bullets of the same nominal diameter.
The Tokarev handgun cartridge from the Soviet Union, also known as the 7.62×25 mm, commonly has a bullet diameter of 0.309 inches, bullet length of 0.52 inches for a 90 grain weight, case diameter of 0.387 inches, cartridge overall length of 1.34 inches, muzzle velocity of 1400-1700 feet per second from a 4.5 inch barrel, ballistic coefficient of 0.142 and an effective range to 50 meters+/−. The well-known rifle cartridge .308 Winchester, also known as 7.62×51 mm NATO, commonly has a bullet diameter of 0.308 inches, bullet length of 1.15 inches for a 165 grain weight, case diameter of 0.470 inches, cartridge overall length of 2.81 inches, muzzle velocity of 2600-2800 feet per second from a 20 inch barrel, ballistic coefficient of 0.450 and an effective range of 800 meters+/−.
Trying to use lighter weight rifle bullets in a pistol application like the Tokarev results in functional compromises or are simply unworkable. Properly seating a tapered nose, longer bullet can extend the cartridge overall length beyond the physical constraints of the magazine and the breech or cannibalize case capacity for the propellant needed to move the bullet at desired velocities.